The Power of DANA: A Year’s Rain in Eight Hours

The term Gota Fría or DANA (Depresión Aislada en Niveles Altos) in Spanish, more commonly called a 'cold drop,' refers to a weather phenomenon for heavy rainfall events that occur specifically on the Spanish Levante and French Mediterranean coast during the autumn.

A Gota Fría sees an upper-level low-pressure system becoming detached from the regular zonal (eastern) circulation and becomes stationary or displays a retrograde (westward) circulation.

The separated 'cut-off' low-pressure system is typically fed by warm air masses from the Mediterranean at its post-summer sea surface temperature peak - which in 2024, reached a record-breaking 28.45 degrees Celsius on August 13.

The region has a long history of catastrophic DANA or similar heavy rainfall-related events across communities in Spain ranging from Valencia, Murcia, and Andalucia.

History of DANA

Incidents included a catastrophic flood on September 11, 1891; 285 milliliters of rainfall in just three hours generated a torrent across Albox, Adra, and smaller towns across Almería's coast and interior that claimed 19 lives, left numerous injuries, and caused immense damage.

In October 1957, Valencia suffered the Great Flood of Valencia. The River Turia overtopped, resulting in significant property damage and killing 81 people. After this flood, in 1969 the Turia was diverted to avoid the city center. If the Turia now floods, most river water is diverted southwards along a new route that borders the city.

In autumn 2024, for the city of Valencia, an upper-level cut-off low-pressure system (DANA) was situated over the Iberian Peninsula from October 26. On October 29, the system generated as much rainfall in the region in eight hours as in the previous twenty months.

Initially impacting the towns and villages in the hills surrounding Valencia, municipalities such as Chiva received 491 millimeters in eight hours, equivalent to a year's worth of rain.

Buñol received 461 millimeters in 24 hours, with similar amounts in Chera, Cheste, and Turís. Newspaper El Paísreported that a heavy storm would see 40-50 millimeters of rainfall - this was ten times as much.

Overwhelmed Ramblas

Ravines or ramblas (dry rivers) help drain rainwater and are vital watercourses to manage excess rain. The Rambla del Poyo runs for 43.5 kilometers (27 miles) from the Parque Natural del Turia mountains and through the city of Valencia to the Mediterranean Sea at Albufera de Valencia.

Located between the main Turia and Júcar rivers and the Picasent ravine, the Rambla basin has an area of 479 square kilometers.

On a typical day, the Rambla del Poyo is dry, or on a rare wet day, a steady flow of water is collected from the surrounding rivers across many neighborhoods.

But with the rainfall of October 29, the Rambla del Poyo saw river flow volume rise by fifty times in the space of a couple of hours, from 45 cubic meters per second at 16:00 local time to 1,726 cubic meters per second by 18:00, peaking at 1,939 cubic meters per second an hour later.

The River Turia running through the city of Valencia coped relatively well, but the Rambla del Poyo was quickly overwhelmed, as a powerful flow of water some two meters higher than its tall banks spread floodwater far and wide, removing concrete bridges, railway tracks, houses, cars, and anything in its path.

On a typical Tuesday evening on Valencia's streets, there was no rain. The rushing floodwater took residents completely by surprise. People on the streets were swept away by fast-moving water.

Submerged cars piled up and flowed downstream, or became stranded on broken highway bridges. Flood water spread into narrow streets engulfing homes and businesses.

So far, the death toll stands at 224, with 216 in Valencia; nearly half were over the age of 70, with bodies found in first-floor apartments, basement garages, and cars, or even on the streets.

Journalist Dominic Hynde reported for Prospect Magazine, and described the aftermath in Valencia:

"I walked for 20 kilometers through the flood-hit areas with a camera and radio microphone, and everyone I spoke to told me the same story. Whole communities have been completely decimated; hundreds of lives lost; countless businesses wiped out. Had the city of Valencia itself not been protected by the Turia flood barriers, it could have been far worse."

The cleanup operation has been overwhelming, with so much major destruction caused, including a thick layer of mud spread over a wide area. On November 6, tens of thousands of Valencia residents took to the streets, frustrated by the slowness of the rescue response from the regional authorities, with pledges of €13 billion.

Spain's public/private Consortium for Insurance Compensation (CCS), responsible for extreme catastrophic events, said it would payout at least €3.5 billion.

According to media reports, various flood mitigation proposals for the Rambla del Poyo have been suggested but not implemented over the last twenty years or so.

These included a plan to reduce flood risks due to be in place in 2011 but dropped due to financial cuts, a plan due to be adopted in 2003 to channel water out of the Rambla del Poyo, a plan to build a pipeline connected to the River Turia to drain flood water, and another plan to build a large reservoir upstream at Cheste, all measures which could have reduced the impact of the floods.

Severe Flooding Around the Mediterranean

It wasn't the only DANA to hit Spain in the last few months. On November 13, Málaga was brought to a standstill, as torrential rain battered the province.

Drenching the Costa del Sol, Guadalhorce Valley, Axarquía, and Málaga City, the region faced over 300 emergency incidents. Physicist Francisco Martín, who had worked for more than 30 years at the Spanish State Meteorological Agency said "I had never seen [two DANAs] or anything like this in my entire professional career."

The Algarve in Portugal experienced severe flooding after reportedly just five minutes of DANA-driven heavy rainfall on November 14, with Albufeira and Moncarapacho among the worst-hit areas, with many homes and businesses submerged.

Across the Mediterranean, in early September, Morocco and Algeria suffered severe flooding, inland from Agadir on Morocco's west coast, the town of Tata saw 10 killed with rainfall totals of 200 millimeters in 24 hours in many locations.

France had the wettest-ever recorded October, with over 700 millimeters of rain in just 48 hours, with the worst-hit regions, Ardèche and Lozère, seeing as much rain in two days as Paris would see in a year.

Inland Flooding Modeling Insights

According to a recent study by Moody's RMS that examined the population at risk of flooding globally, it was found that a non-trivial proportion of Spanish society is at risk from the peril.

At the 100-year defended return period - or with a one percent probability within any given year - the study suggests that about 6.5 million people in Spain are at risk, representing approximately 14 percent of the population.

While defenses are often built intending to protect the population, as well as important economic areas from flooding, the study found that the disparity between the defended and undefended population at risk is quite small with just an additional 300,000, or 6.8 million people at risk when ignoring their impact.

The study also looked at how the proportion of a population affected by flood risk changed over time and into the future. This can help to illustrate whether countries are doing a good job of mitigating the impact of flooding on society, by avoiding developing new properties in flood plains and subsequently seeing reductions in the proportion of population at risk as populations grow, or vice-versa.

Interestingly, while the absolute number at risk has increased, the proportion of Spain's population at risk has not materially changed since 1975, where 4.8 million of its 35.8 million population were at risk, or 13.4 percent. The study finds that this trend is set to continue with a similar percentage at risk in 2030.

Compared with neighboring countries, the study found that Spain has a lower percentage of its population at risk of inland flooding compared with France and Italy.

France has 9.75 million, or 15.2 percent of its population at risk from the peril; Italy has 10.4 million, or 17.5 percent of its population at risk at the 100-year return period - perhaps pointing to a wider problem for other countries around the Mediterranean.

Climate Change Exacerbates

At COP29 in Baku, Kazakhstan, during November, Spanish Prime Minister Pedro Sanchez raised the issue of the Valencia floods, stating that events such as this stress the need for drastic change to rebuild cities to withstand the worst to come, as yet another DANA event impacted the coast of southern and eastern Spain.

Andre Plenkovic, the Croatian Prime Minister, echoed Mr. Sanchez's sentiments in a year that had also seen catastrophic flooding in southern Croatia, and Bosnia and Herzegovina.

World Weather Attribution issued preliminary results after examining the rainfall events in Spain suggesting that these events are about 12 percent more intense and about twice as likely in today's climate, which is 1.3 degrees Celsius warmer than it would have been in the cooler preindustrial climate without human-caused warming.

Although DANAs have been a regular feature of the Mediterranean autumn, the severity of this year's rainfall events has opened up significant vulnerabilities in the ability of the region to cope, adding another issue along with building resilience against flood, severe heat, drought, and wildfire.

Find out about Moody's Global Flood Data and Maps for Spain here, and more about Moody's RMS Europe flood models here.

Daniel Bernet

Assistant Director, Product Management

As an assistant director working in model product management, Daniel is responsible for the Moody's RMS Europe Inland Flood as well as the Europe Severe Convective Storm Models. He has been with Moody's for more than 6 years, joining the company after conducting doctoral and postdoctoral research at the Mobiliar Lab for Natural Risks, University of Bern, focusing on the occurrence and modeling of surface water flooding.

Before academia, he worked for a small Swiss NGO managing different water-related projects in Nepal, following the conclusion of a bachelor's and master's degree in Environmental Engineering at the Swiss Federal Institute of Technology ETH Zurich.

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• #Europe Inland Flood HD Model
• #RMS Global Flood Maps
• #Valencia
• #Spain flood
• #Gota Fría
• #Depresión Aislada en Niveles Altos
• #DANA
• #River Turia
• #ramblas
• #Rambla del Poyo